Methods and apparatus for stenting comprising enhanced embolic protections coupled with improved protections against restenosis and trombus formation

ABSTRACT

Apparatus and methods for stenting are provided comprising a stent attached to a porous biocompatible material that is permeable to endothelial cell ingrowth, but impermeable to release of emboli of predetermined size. Preferred stent designs are provided, as well as preferred manufacturing techniques. Apparatus and methods are also provided for use at a vessel branching. Moreover, embodiments of the present invention may comprise a coating configured for localized delivery of therapeutic agents. Embodiments of the present invention are expected to provide enhanced embolic protection, improved force distribution, and improved recrossability, while reducing a risk of restenosis and thrombus formation.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/859,636, filed on Jun. 3, 2004, which is continuation ofU.S. patent application Ser. No. 09/967,789, filed on Sep. 28, 2001, nowU.S. Pat. No. 6,755,856, which is a continuation-in-part of U.S. patentapplication Ser. No. 09/742,144, filed on Dec. 19, 2000, now U.S. Pat.No. 6,682,554, which is a continuation-in-part of U.S. patentapplication Ser. No. 09/582,318, filed on Jun. 23, 2000, now U.S. Pat.No. 6,602,285, which claims the benefit of the filing date ofInternational Application PCT/EP/99/06456, filed on Sep. 2, 1999, whichclaims priority from German application 19840645.2, filed on Sep. 5,1998, the entireties of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to stents, and more particularly, to stentgrafts having an expandable web structure configured to provide enhancedembolic protection and reduce restenosis and thrombus formation.

BACKGROUND OF THE INVENTION

Stents are commonly indicated for a variety of intravascular andnon-vascular applications, including restoration and/or maintenance ofpatency within a patient's vessel. Stents are also used to reducerestenosis of a blood vessel post-dilation, thereby ensuring adequateblood flow through the vessel. Previously known stents are formed of acell or mesh structure, having apertures through which endothelial cellsmigrate rapidly. These endothelial cells form a smooth coating over thestent that limits interaction between the stent and blood flowingthrough the vessel, thereby minimizing restenosis and thrombusformation.

In many applications, in addition to maintenance of vessel patency andlimitation of restenosis, protection against release of embolic materialfrom the walls of the vessel is desired. Emboli released into thebloodstream flow downstream, where they may occlude flow and causedeath, stroke, or other permanent injury to the patient. The aperturesbetween adjoining cells of previously known stents may provide an avenuefor such embolic release, depending upon the application.

In addition to embolic protection, a smooth surface, i.e. asubstantially continuous surface lacking apertures, may be desired topermit unencumbered recrossability with guide wires, balloon catheters,etc., into the lumen of the stent, for example, to compress stenosis orrestenosis and open the lumen, to resize the stent to accommodatevascular geometry changes, etc. Further, equalization of forces appliedby or to the stent may be desired to reduce a risk of the stent causingvessel dissection. Due to the apertures, previously known stents mayprovide only limited embolic protection, recrossability, and forcedistribution in some applications.

A covered stent, or a stent graft, comprises a stent that is at leastpartially externally-covered, internally-lined, or sintered with abiocompatible material that is impermeable to stenotic emboli. Commoncovering materials include biocompatible polymers, such as polyethyleneterephthalate (PETP or “Dacron”) or expanded polytetrafluoroethylene(ePTFE or “Teflon”). Stent grafts may be either balloon-expandable orself-expanding. Balloon-expandable systems may be expanded to an optimaldiameter in-vivo that corresponds to the internal profile of the vessel.Upon compression, self-expanding embodiments characteristically returnin a resilient fashion to their unstressed deployed configurations andare thus preferred for use in tortuous anatomy and in vessels thatundergo temporary deformation.

A stent graft provides embolic protection by sealing emboli against avessel wall and excluding the emboli from blood flow through the vessel.Additionally, since the biocompatible material of a stent graft closelytracks the profile of the stent, forces applied by and to an impingingvessel wall are distributed over a larger surface area of the stent,i.e. the force is not just applied at discrete points by “struts”located between apertures of the stent. Rather, the biocompatiblematerial also carries the load and distributes it over the surface ofthe stent. Furthermore, stent grafts provide a smooth surface thatallows improved or unencumbered recrossability into the lumen of thegraft, especially when the biocompatible material lines the interior of,or is sintered into, the stent.

While the biocompatible materials used in stent grafts are impermeableto, and provide protection against, embolic release, they typically donot allow rapid endothelialization, because they also are impermeable orsubstantially impermeable to ingrowth of endothelial cells (i.e. havepores smaller than about 30 μm) that form the protective intima layer ofblood vessels. These cells must migrate from the open ends of a stentgraft into the interior of the stent. Migration occurs through bloodflow and through the scaffold provided by the graft. Such migration isslow and may take a period of months, as opposed to the period of daysto weeks required by bare (i.e. non-covered) stents.

In the interim, thrombus may form within the lumen of the graft, withpotentially dire consequences. As a further drawback, migration of theendothelium through the open ends of a graft may leave the endothelialcoating incomplete, i.e. it does not span a mid-portion of the graft. Inaddition, the endothelial layer is often thicker and more irregular thanthe endothelialization observed with bare stents, enhancing the risk ofrestenosis and thrombus formation.

Porous covered stents also are known. For example, U.S. Pat. No.5,769,884 to Solovay describes a covered stent having porous regionsnear the end of the stent, wherein the pores are sized to allow tissueingrowth and endothelialization. The middle region of the stent isdescribed as being much less porous or non-porous, to encapsulatedamaged or diseased tissue and inhibit tissue ingrowth.

The Solovay device is believed to have several drawbacks. First, the endregions of the stent are described as having a preferred pore diameteras large as 120 μm. Pore diameters greater than about 100 μm may provideinadequate embolic protection; thus, if the end regions compress astenosis, hazardous embolization may result. Further, since the middleregion of the stent is adapted to inhibit tissue ingrowth, endothelialcells must migrate into the middle region of the stent from the endregions and from blood flow. As discussed previously, such migration isslow and provides an inferior endothelial layer.

An additional drawback to previously known devices is that many are notconfigured for use at a vessel bifurcation. A bare stent placed across avessel side branch is expected to disrupt flow into the side branch andcreate turbulence that may lead to thrombus formation. Conversely,placement of a non-porous covered stent/stent graft across thebifurcation is expected to permanently exclude the side branch fromblood flow, because such grafts are substantially impermeable to blood.

In view of the drawbacks associated with previously known stents andstent grafts, it would be desirable to provide apparatus and methods forstenting that overcome the drawbacks of previously known devices.

It further would be desirable to provide methods and apparatus thatreduce the risk of embolic release, while also reducing the risk ofrestenosis and thrombus formation.

It also would be desirable to provide apparatus and methods for stentingthat allow improved recrossability into the lumen of the apparatus.

It would be desirable to provide apparatus and methods for stenting thatdistribute forces applied by or to the apparatus.

It still further would be desirable to provide apparatus and methodssuitable for use in bifurcated vessels.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide apparatus and methods for stenting that overcome the drawbacksof previously known apparatus and methods.

It is an object to reduce the risk of embolic release during and afterstenting, and also reduce the risk of restenosis and thrombus formation.

It is yet another object of the present invention to provide apparatusand methods that allow unencumbered recrossability into the lumen of theapparatus.

It is an object to provide apparatus and methods for stenting thatdistribute forces applied by or to the apparatus.

It is an object to provide apparatus and methods suitable for use in abifurcated vessel.

These and other objects of the present invention are accomplished byproviding apparatus comprising a stent, for example, aballoon-expandable, a self-expanding, a bistable cell, or a metal meshstent. A biocompatible material at least partially is sintered betweenthe apertures of the stent, or covers the interior or exterior surface(or both) of the stent. Unlike previously known stent grafts,embodiments of the present invention are both permeable to ingrowth andimpermeable to release of critical-sized emboli along their entirelengths. Thus, the present invention provides the embolic protection,force distribution, and improved recrossability characteristic ofnon-porous stent grafts, while further providing the protection againstrestenosis and thrombus formation characteristic of bare stents.

In one preferred embodiment, the biocompatible material of the presentinvention comprises, for example, a porous woven, knitted, or braidedmaterial having pore sizes determined as a function of the tightness ofthe weave, knit, or braid. Pore size is selected to allow endothelialcell ingrowth, while preventing release of emboli larger than apredetermined size. In an alternative embodiment, the biocompatiblematerial comprises pores that are chemically, physically, mechanically,laser-cut, or otherwise created through the material with a specifieddiameter, spacing, etc. The pores may be provided with uniform ornon-uniform density, size, and/or shape. The pores preferably have aminimum width large enough to promote endothelial cell ingrowth, and amaximum width small enough to reduce the risk of embolic release.

Apparatus also is provided for use in a bifurcated or branched vessel.Since the porous biocompatible material of the present invention ispermeable to blood flow, it is expected that, when implanted, flow intoa side branch will continue uninterrupted. The small diameter of thepores, relative to the diameter of the stent apertures, will provide agrating that is expected to minimize turbulence and allow thrombus-freeblood flow into the side branch. Optionally, the porosity, i.e. thediameter, density, shape, and/or arrangement, of the pores may bealtered in the region of the side branch to ensure adequate flow.

Alternatively, the stent and biocompatible material may comprise aradial opening. When stenting at a vessel bifurcation or branching, theradial opening may be positioned in line with the side branch tomaintain patency of the branch. Alternatively, a plurality of radialopenings may be provided along the length of the implant to facilitatecontinuous blood flow through a plurality of side branches.

Stents for use with apparatus of the present invention preferablycomprise a tubular body with a wall having a web structure configured toexpand from a contracted delivery configuration to an expanded deployedconfiguration. The web structure comprises a plurality of neighboringweb patterns having adjoining webs. Each web has three sections: acentral section arranged substantially parallel to the longitudinal axisin the contracted delivery configuration, and two lateral sectionscoupled to the ends of the central section. The angles between thelateral sections and the central section increase during expansion,thereby reducing or substantially eliminating length decrease of thestent due to expansion, while increasing a radial stiffness of thestent.

Preferably, each of the three sections of each web is substantiallystraight, the lateral sections preferably define obtuse angles with thecentral section, and the three sections are arranged relative to oneanother to form a concave or convex structure. When contracted to itsdelivery configuration, the webs resemble stacked or nested bowls orplates. This configuration provides a compact delivery profile, as thewebs are packed against one another to form web patterns resembling rowsof the stacked plates.

Neighboring web patterns are preferably connected to one another byconnection elements preferably formed as straight sections. In apreferred embodiment, the connection elements extend between adjacentweb patterns from the points of interconnection between neighboring webswithin a given web pattern.

The orientation of connection elements between a pair of neighboring webpatterns preferably is the same for all connection elements disposedbetween the pair. However, the orientation of connection elementsalternates between neighboring pairs of neighboring web patterns. Thus,a stent illustratively flattened and viewed as a plane provides analternating orientation of connection elements between the neighboringpairs: first upwards, then downwards, then upwards, etc.

As will be apparent to one of skill in the art, positioning,distribution density, and thickness of connection elements and adjoiningwebs may be varied to provide stents exhibiting characteristics tailoredto specific applications. Applications may include, for example, use inthe coronary or peripheral (e.g. renal) arteries. Positioning, density,and thickness may even vary along the length of an individual stent inorder to vary flexibility and radial stiffness characteristics along thelength of the stent.

Stents for use with apparatus of the present invention preferably areflexible in the delivery configuration. Such flexibility beneficiallyincreases a clinician's ability to guide the stent to a target sitewithin a patient's vessel. Furthermore, stents of the present inventionpreferably exhibit high radial stiffness in the deployed configuration.Implanted stents therefore are capable of withstanding compressiveforces applied by a vessel wall and maintaining vessel patency. The webstructure described hereinabove provides the desired combination offlexibility in the delivery configuration and radial stiffness in thedeployed configuration. The combination further may be achieved, forexample, by providing a stent having increased wall thickness in a firstportion of the stent and decreased wall thickness with fewer connectionelements in an adjacent portion or portions of the stent.

Embodiments of the present invention may comprise a coating or attachedactive groups configured for localized delivery of radiation, genetherapy, medicaments, thrombin inhibitors, or other therapeutic agents.Furthermore, embodiments may comprise one or more radiopaque features tofacilitate proper positioning within a vessel.

Methods of using the apparatus of the present invention also areprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention, its nature and various advantages,will be more apparent from the following detailed description of thepreferred embodiments, taken in conjunction with the accompanyingdrawings, in which like reference numerals apply to like partsthroughout, and in which:

FIG. 1 is a schematic isometric view illustrating the basic structure ofa preferred stent for use with apparatus of the present invention;

FIG. 2 is a schematic view illustrating a web structure of a wall of thestent of FIG. 1 in a contracted delivery configuration;

FIG. 3 is a schematic view illustrating the web structure of the stentof FIG. 1 in an expanded deployed configuration;

FIG. 4 is an enlarged schematic view of the web structure in thedelivery configuration;

FIG. 5 is a schematic view of an alternative web structure of the stentof FIG. 1 having transition sections and shown in an as-manufacturedconfiguration;

FIGS. 6A-6C are side-sectional views of a prior art bare stent in anexpanded deployed configuration within a patient's vasculature,illustrating limitations of bare stents with regard to embolicprotection, recrossability, and force distribution, respectively;

FIG. 7 is a side-sectional view of a prior art, non-porous stent graftin an expanded deployed configuration within a patient's vasculature,illustrating the potential for thrombus formation and restenosis due toinefficient endothelial cell migration;

FIGS. 8A and 8B are side-sectional views of a first embodiment ofapparatus of the present invention, shown, respectively, in a collapseddelivery configuration and in a deployed configuration;

FIGS. 9A-9D are side-sectional views of the apparatus of FIGS. 8A-8Bwithin a patient's vasculature, illustrating a method of using theapparatus in accordance with the present invention;

FIGS. 10A-10C are side-sectional views of the apparatus of FIGS. 8A-8Bwithin a patient's vasculature, illustrating capacity for reintroductioninto the lumen of the apparatus and a method for establishing orrestoring vessel patency after implantation of the apparatus;

FIG. 11 is a side-sectional view of the apparatus of FIGS. 8A-8B withina patient's vasculature illustrating force distribution upon interactionwith an impinging vessel;

FIG. 12 is a side-sectional view of the apparatus of FIGS. 8A-8B in useat a vessel branching;

FIG. 13 is a side-sectional view of an alternative embodiment ofapparatus of the present invention comprising a radial opening, in useat a vessel branching;

FIGS. 14A and 14B are cross-sectional views, illustrating stent/stentcovering attachment schemes; and

FIGS. 15A-15D are isometric schematic views illustrating varioustechniques for attaching a stent covering to a stent in a manner thatprovides the attachment scheme of FIG. 14B.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to stent grafts having an expandable webstructure, the stent grafts being configured to provide enhanced embolicprotection and improved protection against restenosis and thrombusformation. These attributes are attained by attaching to a stent abiocompatible material that is impermeable to emboli but permeable toingrowth of endothelial cells. Attaching the material to the stent alsodistributes forces applied to or by the apparatus, and facilitatesrecrossing into the lumen of the apparatus post-implantation with guidewires, balloons, etc. Thus, unlike previously known bare stents, thepresent invention provides improved protection against embolic release,a smoother surface for recrossing, and better distribution of forcesapplied to or by the apparatus. Moreover, unlike previously known,non-porous stent grafts, the present invention provides enhancedprotection against thrombus formation and restenosis via rapidendothelialization.

Prior to a detailed presentation of embodiments of the presentinvention, preferred stent designs for use with such embodiments areprovided in FIGS. 1-5. Stent 1 of FIG. 1 is as described in co-pendingU.S. patent application Ser. No. 09/742,144, filed Dec. 19, 2000, whichis incorporated herein by reference. Stent 1 comprises tubular flexiblebody 2 having wall 3. Wall 3 comprises a web structure describedhereinbelow with respect to FIGS. 2-5.

Stent 1 and its web structure are expandable from a contracted deliveryconfiguration to an expanded deployed configuration. Depending on thematerial of fabrication, stent 1 may be either self-expanding orexpandable using a balloon catheter. If self-expanding, the webstructure is preferably fabricated from a superelastic material, such asa nickel-titanium alloy. Furthermore, stent 1 preferably is fabricatedfrom biocompatible and/or biodegradable materials. It also may beradiopaque to facilitate delivery, and it may comprise an externalcoating that, for example, retards thrombus formation or restenosiswithin a vessel. The coating alternatively may deliver therapeuticagents into the patient's blood stream.

With reference to FIGS. 2-4, a first embodiment of the web structure ofstent 1 is described. In FIGS. 2-4, wall 3 of body 2 of stent 1 is shownflattened into a plane for illustrative purposes. FIG. 2 shows webstructure 4 in a contracted delivery configuration, with line Lindicating the longitudinal axis of the stent. Web structure 4 comprisesneighboring web patterns 5 and 6 arranged in alternating, side-by-sidefashion. Thus, the web patterns seen in FIG. 2 are arranged in thesequence 5, 6, 5, 6, 5, etc.

FIG. 2 illustrates that web patterns 5 comprise adjoining webs 9(concave up in FIG. 2), while web patterns 6 comprise adjoining webs 10(convex up in FIG. 2). Each of these webs has a concave or convex shaperesulting in a stacked plate- or bowl-like appearance when the stent iscontracted to its delivery configuration. Webs 9 of web patterns 5 arerotated 180 degrees with respect to webs 10 of web patterns 6, i.e.,alternating concave and convex shapes. The structure of webs 9 and 10 isdescribed in greater detail hereinbelow with respect to FIG. 4.

Neighboring web patterns 5 and 6 are interconnected by connectionelements 7 and 8. A plurality of connection elements 7 and 8 areprovided longitudinally between each pair of web patterns 5 and 6.Multiple connection elements 7 and 8 are disposed in the circumferentialdirection between adjacent webs 5 and 6. The position, distributiondensity, and thickness of these pluralities of connection elements maybe varied to suit specific applications in accordance with the presentinvention.

Connection elements 7 and 8 exhibit opposing orientation. However, allconnection elements 7 preferably have the same orientation that, as seenin FIG. 2, extends from the left side, bottom, to the right side, top.Likewise, all connection elements 8 preferably have the same orientationthat extends from the left side, top, to the right side, bottom.Connection elements 7 and 8 alternate between web patterns 5 and 6, asdepicted in FIG. 2.

FIG. 3 illustrates the expanded deployed configuration of stent 1, againwith reference to a portion of web structure 4. When stent 1 is in theexpanded deployed configuration, web structure 4 provides stent 1 withhigh radial stiffness. This stiffness enables stent 1 to remain in theexpanded configuration while, for example, under radial stress. Stent 1may experience application of radial stress when, for example, implantedinto a hollow vessel in the area of a stenosis.

FIG. 4 is an enlarged view of web structure 4 detailing a portion of theweb structure disposed in the contracted delivery configuration of FIG.2. FIG. 4 illustrates that each of webs 9 of web pattern 5 comprisesthree sections 9 a, 9 b and 9 c, and each of webs 10 of web pattern 6comprises three sections 10 a, 10 b and 10 c. Preferably, eachindividual section 9 a, 9 b, 9 c, 10 a, 10 b and 10 c, has a straightconfiguration.

Each web 9 has a central section 9 b connected to lateral sections 9 aand 9 c, thus forming the previously mentioned bowl- or plate-likeconfiguration. Sections 9 a and 9 b enclose obtuse angle α. Likewise,central section 9 b and lateral section 9 c enclose obtuse angle β.Sections 10 a-10 c of each web 10 of each web pattern 6 are similarlyconfigured, but are rotated 180 degrees with respect to correspondingwebs 9. Where two sections 9 a or 9 c, or 10 a or 10 c adjoin oneanother, third angle γ is formed (this angle is zero where the stent isin the fully contracted position, as shown in FIG. 4).

Preferably, central sections 9 b and 10 b are substantially aligned withthe longitudinal axis L of the tubular stent, when the stent is in thecontracted delivery configuration. The angles between the sections ofeach web increase in magnitude during expansion to the deployedconfiguration, except that angle γ, which is initially zero or acute,approaches a right angle after deployment of the stent. This increaseprovides high radial stiffness with reduced shortening of the stentlength during deployment. As will of course be understood by one ofordinary skill in the art, the number of adjoining webs that span acircumference of the stent preferably is selected corresponding to thevessel diameter in which the stent is to be implanted.

FIG. 4 illustrates that, with stent 1 disposed in the contracteddelivery configuration, webs 9 adjoin each other in an alternatingfashion and are each arranged like plates stacked into one another, asare adjoining webs 10. FIG. 4 further illustrates that the configurationof the sections of each web applies to all of the webs, which jointlyform web structure 4 of wall 3 of tubular body 2 of stent 1. Webs 9 areinterconnected within each web pattern 5 via rounded connection sections12, of which one connection section 12 is representatively labeled. Webs10 of each neighboring web pattern 6 are similarly configured.

FIG. 4 also once again demonstrates the arrangement of connectionelements 7 and 8. Connection elements 7, between a web pattern 5 and aneighboring web pattern 6, are disposed obliquely relative to thelongitudinal axis L of the stent with an orientation A, which is thesame for all connection elements 7. Orientation A is illustrated by astraight line that generally extends from the left side, bottom, to theright side, top of FIG. 4. Likewise, the orientation of all connectionelements 8 is illustrated by line B that generally extends from the leftside, top, to the right side, bottom of FIG. 4. Thus, an alternating A,B, A, B, etc., orientation is obtained over the entirety of webstructure 4 for connection elements between neighboring web patterns.

Connection elements 7 and 8 are each configured as a straight sectionthat passes into a connection section 11 of web pattern 5 and into aconnection section 11′ of web pattern 6. This is illustratively shown inFIG. 4 with a connection element 7 extending between neighboringconnection sections 11 and 11′, respectively. It should be understoodthat this represents a general case for all connection elements 7 and 8.

Since each web consists of three interconnected sections that formangles α and β with respect to one another, which angles are preferablyobtuse in the delivery configuration, expansion to the deployedconfiguration of FIG. 3 increases the magnitude of angles α and β. Thisangular increase beneficially provides increased radial stiffness in theexpanded configuration. Thus, stent 1 may be flexible in the contracteddelivery configuration to facilitate delivery through tortuous anatomy,and also may exhibit sufficient radial stiffness in the expandedconfiguration to ensure vessel patency, even when deployed in an area ofstenosis. The increase in angular magnitude also reduces and may evensubstantially eliminate length decrease of the stent due to expansion,thereby decreasing a likelihood that stent 1 will not completely span atarget site within a patient's vessel post-deployment.

The stent of FIG. 4 is particularly well suited for use as aself-expanding stent when manufactured, for example, from a shape memoryalloy such as nickel-titanium. In this case, web patterns 5 and 6preferably are formed by laser-cutting a tubular member, whereinadjacent webs 9 and 10 are formed using slit-type cuts. Only the areascircumferentially located between connection members 7 and 8 (shadedarea D in FIG. 4) require removal of areas of the tubular member. Theseareas also may be removed from the tubular member using laser-cuttingtechniques.

Referring now to FIG. 5, an alternative embodiment of the web structureof stent 1 is described. FIG. 5 shows the alternative web structure inan as-manufactured configuration. The basic pattern of the embodiment ofFIG. 5 corresponds to that of the embodiment of FIGS. 2-4. Thus, thisalternative embodiment also relates to a stent having a tubular flexiblebody with a wall having a web structure that is configured to expandfrom a contracted delivery configuration to a deployed configuration.

Likewise, the web structure again comprises a plurality of neighboringweb patterns, of which two are illustratively labeled in FIG. 5 as webpatterns 5 and 6. Web patterns 5 and 6 are again provided with adjoiningwebs 9 and 10, respectively. Each of webs 9 and 10 is subdivided intothree sections, and reference is made to the discussion providedhereinabove, particularly with respect to FIG. 4. As will of course beunderstood by one of skill in the art, the stent of FIG. 5 will have asmaller diameter when contracted (or crimped) for delivery, and may havea larger diameter than illustrated in FIG. 5 when deployed (or expanded)in a vessel.

The embodiment of FIG. 5 differs from the previous embodiment by theabsence of connection elements between web patterns. In FIG. 5, webpatterns are interconnected to neighboring web patterns by transitionsections 13, as shown by integral transition section 13 disposed betweensections 9 c and 10 c. Symmetric, inverted web patterns are therebyobtained in the region of transition sections 13. To enhance stiffness,transition sections 13 preferably have a width greater than twice thewidth of webs 9 or 10.

As seen in FIG. 5, every third neighboring pair of webs 9 and 10 isjoined by an integral transition section 13. As will be clear to thoseof skill in the art, the size and spacing of transition sections 13 maybe altered in accordance with the principles of the present invention.

An advantage of the web structure of FIG. 5 is that it provides stent 1with compact construction coupled with a high degree of flexibility inthe delivery configuration and high load-bearing capabilities in thedeployed configuration. Furthermore, FIG. 5 illustrates that, as withconnection elements 7 and 8 of FIG. 4, transition sections 13 have analternating orientation and are disposed obliquely relative to thelongitudinal axis of the stent (shown by reference line L). FIG. 5 alsoillustrates that, especially in the deployed configuration, an H-likeconfiguration of transition sections 13 with adjoining web sections isobtained.

The stent of FIG. 5 is well suited for use as a balloon-expandablestent, and may be manufactured from stainless steel alloys. Unlike thestent of FIG. 4, which is formed in the contracted deliveryconfiguration, the stent of FIG. 5 preferably is formed in a partiallydeployed configuration by removing the shaded areas D′ between webs 9and 10 using laser-cutting or chemical etching techniques. In this case,central sections 9 b and 10 b are substantially aligned with thelongitudinal axis L of the stent when the stent is crimped onto thedilatation balloon of a delivery system.

As will be apparent to one of skill in the art, positioning,distribution density, and thickness of connection elements and adjoiningwebs may be varied to provide stents exhibiting characteristics tailoredto specific applications. Applications may include, for example, use inthe coronary or peripheral (e.g. renal) arteries. Positioning, density,and thickness may even vary along the length of an individual stent inorder to flexibility and radial stiffness characteristics along thelength of the stent.

Stents of the present invention preferably are flexible in the deliveryconfiguration. Such flexibility beneficially increases a clinician'sability to guide the stent to a target site within a patient's vessel.Furthermore, stents of the present invention preferably exhibit highradial stiffness in the deployed configuration. Implanted stentstherefore are capable of withstanding compressive forces applied by avessel wall and maintain vessel patency. The web structure describedhereinabove provides the desired combination of flexibility in thedelivery configuration and radial stiffness in the deployedconfiguration. The combination further may be achieved, for example, byproviding a stent having increased wall thickness in a first portion ofthe stent and decreased wall thickness with fewer connection elements inan adjacent portion or portions of the stent.

Referring now to FIGS. 6 and 7, limitations of previously knownapparatus are described prior to the detailed description of embodimentsof the present invention. In FIGS. 6A-6C, limitations of a previouslyknown bare stent are described. As seen in FIG. 6A, stent 14 has beenimplanted within a patient's vessel V at a treatment site exhibitingstenosis S, using well-known techniques. Stent 14 has lumen 15 andcomprises cell or mesh structure 16 having apertures 17. Stent 14 isshown expanded, e.g. either resiliently or via a balloon, to compressstenosis S against the wall of vessel V and restore patency within thevessel. During compression of stenosis S, particles break away from thestenosis to form emboli E. These emboli escape from the vessel wallthrough apertures 17 of stent 14. Blood flowing through vessel V indirection D carries the released emboli E downstream, where the embolimay occlude flow and cause death, stroke, or other permanent injury tothe patient. Stent 14 therefore may provide inadequate embolicprotection, depending upon the specific application.

In FIG. 6B, stent 14 has been implanted for an extended period of timein vessel V across a stenosed region. Restenosis R has formed withinlumen 15 of stent 14, requiring further reintervention to restorepatency to the vessel. Apertures 17 of stent 14 provide the stent with anon-uniform surface that complicates recrossing of the stent with guidewires, angioplasty balloons, etc., post-implantation.

In FIG. 6B, guide wire G has been advanced through the patient'svasculature into lumen 15 of stent 14 to provide a guide for advancementof an angioplasty balloon to compress restenosis R and reopen vessel V.Distal tip T of guide wire G has become entangled within structure 16 ofstent 14 during recrossing, because the wire has inadvertently passedthrough an aperture 17. If guide wire G becomes caught on structure 16,emergency surgery may be necessary to remove the guide wire.Alternatively, a portion of guide wire G (or a portion of any otherdevice inserted post-implantation through lumen 15 and entangled withinstent 14) may break off from the guide wire and remain within thevessel, presenting a risk for thrombus formation or vessel dissection.

In addition to the problems associated with recrossing bare stent 14upon restenosis, if stent 14 is self-expanding, the stent may provideinadequate radial force to compress a vessel stenosis at the time ofimplantation (not shown). Recrossing lumen 15 of stent 14 with a ballooncatheter then may be necessary to compress the stenosis and fully openthe lumen (not shown). As illustrated in FIG. 6B, such recrossing may bedifficult or impossible.

In FIG. 6C, stent 14 has been implanted into vessel V that is subject totemporary deformation, for example, due to contact with neighboringmuscles, due to joint motion, or due to external pressure applied to thevessel. The wall of vessel V impinges on a single strut 18 of structure16 of stent 14. Since all force is concentrated at the point ofimpingement of vessel V and strut 18, strut 18 punctures vessel V atsite P. Alternatively, temporary deformation of vessel V may kink stent14 at strut 18, thus reducing lumen 15 and decreasing the utility ofstent 14 (not shown). Clearly, either of these conditions may create aserious risk to the health of the patient. Similarly, stent 10 maydissect the vessel wall or may kink if implanted in tortuous anatomy(not shown). It would therefore be desirable to modify stent 14 tobetter distribute loads applied to the stent.

Referring now to FIG. 7, limitations of a previously known, non-porouscovered stent, or stent graft, are described. Stent graft 20 comprisesballoon-expandable or self-expanding stent 22 having lumen 23. Stent 22comprises cell or mesh structure 24 having apertures 26. The stent iscovered with biocompatible material 28, which commonly comprises abiocompatible polymer, such as PTFE, PETP, or a homologic material.Biocompatible material 28 is beneficially impermeable to stenoticemboli, but detrimentally impermeable to endothelial cell ingrowth.

In FIG. 7, graft 20 has been implanted for an extended period of time,for example, a period of months, within vessel V. Unlike stent 14 ofFIG. 6, endothelial cells are not able to rapidly migrate throughapertures 26 of stent 22 and surround graft 20 with a thin, uniformlayer of endothelial cells that limit interaction between the graft andblood flowing through the vessel, thereby reducing restenosis andthrombus formation. Rather, since biocompatible material 28 isimpermeable to ingrowth of the endothelial cells that form theprotective intima layer of blood vessels, these cells must migrate fromthe open ends of graft 20 into the interior of lumen 23.

Migration occurs via blood flowing through vessel V in direction D andvia the scaffold provided by the body of graft 20. However, thismigration is slow and may take a period of months, as opposed to theperiod of days to weeks required for endothelialization of bare stents.Furthermore, as illustrated by endothelial layer E in FIG. 7, migrationthrough the open ends of graft 20 may provide an incomplete endotheliallayer, i.e. a layer that does not span a mid-portion of the graft. LayerE also may be thicker and more irregular than the endothelial layerobtained with bare stents. Gaps, irregularity, and thickening in layerE, as well as extended time required for formation of layer E, may yieldthrombus T or restenosis within lumen 23 of graft 20, with potentiallydire consequences. Stent graft 20 therefore may not provide adequateprotection against restenosis and thrombus formation.

Referring now to FIGS. 8A and 8B, a first embodiment of apparatus of thepresent invention is described in detail. Apparatus 30 comprises stent32 having lumen 33. Stent 32 may be, for example, self-expanding orballoon-expandable, or may be of bistable cell or metal meshconstruction. Stent 32 comprises cell or mesh structure 34 withapertures 36. In a preferred embodiment, stent 32 comprises the designof stent 1, described hereinabove with respect to FIGS. 1-5. Stent 32may further comprise an anchoring feature, such as hook or barb 35, tofacilitate attachment to a vessel wall. The anchoring featurealternatively may comprise structure 34, which interacts with the vesselwall, for example, by pressing against the wall or by endothelial cellingrowth into the structure, to anchor stent 32. Biocompatible material38 having pores 39 is attached to at least a portion of stent 32.

Unlike material 28 of stent graft 20 (and unlike the material describedhereinabove with respect to U.S. Pat. No. 5,769,884 to Solovay),material 38 of apparatus 30 is both permeable to endothelial cellingrowth and impermeable to release of emboli of predetermined size,e.g. larger than about 100 μm, along its entire length. Thus, like stentgraft 20 of FIG. 7, apparatus 30 provides enhanced embolic protection,improved force distribution, and improved recrossability; furthermore,like bare stent 14 of FIG. 6, apparatus 30 provides enhanced protectionagainst restenosis and thrombus formation.

Biocompatible material 38 may comprise a biocompatible polymer, forexample, a modified thermoplastic Polyurethane, polyethyleneterephthalate, polyethylene tetraphthalate, expandedpolytetrafluoroethylene, polypropylene, polyester, Nylon, polyethylene,polyurethane, or combinations thereof. Alternatively, biocompatiblematerial 38 may comprise a homologic material, such as an autologous ornon-autologous vessel. Further still, material 38 may comprise abiodegradable material, for example, polylactate or polyglycolic acid.In FIG. 8, material 38 illustratively lines the interior surface ofstent 32, but it should be understood that material 38 alternatively maycover the stent's exterior surface, may be sintered within apertures 36of stent 32, or may otherwise be attached to the stent.

Material 38 preferably comprises a woven, knitted, or braided material,wherein the size of pores 39 is determined as a function of thetightness of the weave, knit, or braid. The size of pores 39 then may bespecified to allow endothelial cell ingrowth, while preventing releaseof emboli larger than a critical dangerous size, for example, largerthan about 100 μm. In an alternative embodiment, the biocompatiblematerial comprises pores 39 that are chemically, physically,mechanically, or laser cut, or otherwise created through material 38with a specified diameter, spacing, etc.

Pores 39 may be provided with uniform or non-uniform density, size,and/or shape. The pores preferably have a minimum width no smaller thanapproximately 30 μm and a maximum width no larger than approximately 100μm. Widths smaller than about 3 μm are expected to inhibit endothelialcell ingrowth, while widths larger than about 100 μm are expected toprovide inadequate embolic protection, i.e. emboli of dangerous size maybe released into the blood stream. Each of pores 39 is even morepreferably provided with a substantially uniform, round shape having adiameter of approximately 80 μm. Pores 39 preferably are located alongthe entire length of material 38.

Stent 32 may be fabricated from a variety of materials. Ifself-expanding, the stent preferably comprises a superelastic material,such as a nickel-titanium alloy, spring steel, or a polymeric material.Alternatively, stent 32 may be fabricated with a resilient knit orwickered weave pattern of elastic materials, such as stainless steel. Ifballoon-expandable, metal mesh, or bistable cell, stent 32 is preferablyfabricated from elastic materials, such as stainless steel or titanium.

At least a portion of stent 32 preferably is radiopaque to facilitateproper positioning of apparatus 30 within a vessel. Alternatively,apparatus 30, or a delivery system for apparatus 30 (see FIG. 9), maycomprise a radiopaque feature, for example, optional radiopaque markerbands 40, to facilitate positioning. Marker bands 40 comprise aradiopaque material, such as gold or platinum.

Apparatus 30 also may comprise coatings or attached active groups Cconfigured for localized delivery of radiation, gene therapy,medicaments, thrombin inhibitors, or other therapeutic agents. Coatingsor active groups C may, for example, be absorbed or adsorbed onto thesurface, may be attached physically, chemically, biologically,electrostatically, covalently, or hydrophobically, or may be bonded tothe surface through Van der Waal's forces, or combinations thereof,using a variety of techniques that are well-known in the art.

In FIG. 8A, apparatus 30 is shown in a collapsed delivery configuration,while, in FIG. 8B, apparatus 30 is in an expanded deployedconfiguration. If stent 32 is self-expanding, apparatus 30 may becollapsed to the delivery configuration over a guide wire or elongatedmember, and then covered with a sheath to maintain the apparatus in thedelivery configuration. Using well-known percutaneous techniques,apparatus 30 is advanced through a patient's vasculature to a treatmentsite, where the sheath is withdrawn; stent 32 dynamically self-expandsto the deployed configuration of FIG. 8B (see FIG. 9). If stent 32 isballoon expandable, apparatus 30 may be mounted in the deliveryconfiguration on a balloon catheter, for delivery to the treatment site.Upon delivery using well-known techniques, the balloon catheter isinflated with sufficient pressure to facilitate irreversible expansionof the apparatus to the deployed configuration (not shown).

With reference to FIGS. 9A-9D, a method of using the apparatus of FIG. 8within a patient's vasculature is described in detail. In FIG. 9, stent32 of apparatus 30 is illustratively self-expanding. However, it shouldbe understood that stent 32 alternatively may be, for example,balloon-expandable, or be made from bistable cells or a metal mesh, inaccordance with the present invention.

In FIG. 9A, vessel V is partially occluded with stenosis S that disruptsblood flow in direction D. Using well-known techniques, apparatus 30,disposed in the collapsed delivery configuration over elongated member52 and constrained in that configuration by sheath 54 of delivery system50, is advanced to the point of stenosis, as seen in FIG. 9B.Radiopacity of stent 32, viewed under a fluoroscope, may facilitateproper positioning of apparatus 30 within the vessel. Alternatively,radiopaque marker bands 40, illustratively disposed on sheath 54, mayfacilitate positioning.

In FIG. 9C, sheath 54 is retracted proximally with respect to elongatedmember 52, thereby allowing apparatus 30 to dynamically self-expand tothe deployed configuration. Apparatus 30 compresses and traps stenosis Sagainst the wall of vessel V. Optional barb or hook 35 of stent 32facilitates anchoring of stent 32 to vessel V. The controlled size ofpores 39 along the length of apparatus 30 ensures that dangerous emboli,broken away from stenosis S during compression, do not escape from thevessel wall and enter the bloodstream. Apparatus 30 protects againstembolization at the time of implantation, and further protects againstdelayed stroke caused by late embolization.

As seen in FIG. 9D, delivery system 50 is removed from the vessel. Pores39 allow endothelial cells to rapidly migrate through apertures 36 ofstent 32 and into the interior of apparatus 30 to form endothelial layerE over the entirety of apparatus 30. Layer E forms, for example, over aperiod of days to weeks. Unlike the endothelial layer covering stentgraft 20 in FIG. 7, endothelial layer E of apparatus 30 is expected toform rapidly, to be complete, thin, and substantially regular. Layer Eacts as a protective layer that reduces adverse interaction betweenapparatus 30 and the patient, thereby lessening the risk of thrombusformation and restenosis. Thus, in addition to maintaining patency ofvessel V, apparatus 30 provides embolic protection coupled with reducedlikelihood of restenosis and thrombus formation. Furthermore, optionalcoating or attached active groups C of material 38 may deliverradiation, gene therapy, medicaments, thrombin inhibitors, or othertherapeutic substances to the vessel wall, or directly into the bloodstream.

Apparatus 30 compresses and seals stenosis S against the wall of vesselV, thereby preventing embolic material from the stenosis from travelingdownstream. Alternatively, via angioplasty or other suitable means,stenosis S may be compressed against the vessel wall prior to insertionof apparatus 30, in which case apparatus 30 still protects againstdelayed stroke caused by late embolization. In addition to theapplication of FIG. 9, apparatus 30 may be used for a variety of otherapplications, including, but not limited to, bridging defective pointswithin a vessel, such as aneurysms, ruptures, dissections, punctures,etc.

While the rapid endothelialization of apparatus 30, discussed withrespect to FIG. 9D, minimizes risk of restenosis and thrombus formation,restenosis may still occur in a limited number of patients.Additionally, vessel V may become lax and expand to a larger diameter.Under these and other circumstances, it may be necessary to recrosslumen 33 of apparatus 30 with interventional instruments. Theseinstruments may, for example, adjust apparatus 30, restore patency tovessel V in an area of restenosis, treat vascular complications distalto apparatus 30, or facilitate any of a variety of other minimallyinvasive procedures.

Referring now to FIGS. 10A-10C, capacity for recrossing with apparatus30 is described. As in FIGS. 9A-9D, stent 32 of apparatus 30 isillustratively self-expandable. In FIG. 10A, stent 32 has been implantedin vessel V using the techniques described hereinabove with respect toFIGS. 9A-9C. However, in contrast to FIG. 9C, stent 32 comprisesinsufficient radial strength to fully compress and seal stenosis Sagainst the wall of vessel V. Guide wire G is therefore advanced throughlumen 33 to provide a guide for advancement of a balloon catheter tofully compress stenosis S. The smooth interior surface provided bybiocompatible material 38 of apparatus 30 ensures that guide wire G mayrecross lumen 33 without becoming entangled in the stent, as wasdescribed hereinabove with respect to FIG. 6B.

In FIG. 10B, once guide wire G has recrossed lumen 33, balloon catheter60 is advanced over guide wire G to the point of stenosis S. Balloon 62of catheter 60 is inflated with sufficient pressure to compress stenosisS against the walls of vessel V and fully deploy apparatus 30. As seenin FIG. 10C, balloon 62 is then deflated, and catheter 60 is removedfrom vessel V, thereby restoring patency to the vessel. Endotheliallayer E then rapidly forms via endothelial cells that migrate throughapertures 36 of stent 32 and pores 39 of material 38 into the interiorof apparatus 30.

As will be apparent to those of skill in the art, recrossing ofapparatus 30 may be indicated in a variety of applications, in additionto those of FIG. 10. For example, apparatus 30 may be recrossed in orderto compress restenosis that has formed within the vessel, as illustratedwith bare stent 14 in FIG. 6B. Additionally, apparatus 30 may berecrossed in order to resize the apparatus so that it conforms to, oraccommodates changes in, vessel geometry.

With reference now to FIG. 11, apparatus 30 has been implanted intovessel V that is undergoing temporary deformation, for example, due tocontact with neighboring muscles, due to joint motion, or due toexternal pressure applied to the vessel. The wall of vessel V impingeson apparatus 30. In contrast to bare stent 14 of FIG. 6C, apparatus 30distributes the load applied by vessel V across adjoining cells ofstructure 34 of stent 32, and across the section of biocompatiblematerial 38 attached to the adjoining cells. Thus, the constrictedportion of vessel V neither collapses within lumen 33 of apparatus 30nor is punctured by apparatus 30. Additionally, since the load isdistributed, stent 32 of apparatus 30 does not kink, and lumen 33remains patent. Similarly, apparatus 30 is expected to continue tofunction safely and properly if implanted in tortuous anatomy.

Referring to FIG. 12, apparatus 30 is shown in use in a branched orbifurcated vessel. Using well-known techniques, apparatus 30 has beenexpanded to the deployed configuration within common carotid artery CCAand external carotid artery ECA. Internal carotid artery ICA branchesoff from the common carotid. Uninterrupted and unimpeded blood flowthrough the side branch presented by internal carotid artery ICA must bemaintained when stenting in the common carotid artery CCA and externalcarotid artery ECA. Since pores 39 of biocompatible material 38 renderapparatus 30 permeable to blood flow, continued blood flow into internalcarotid artery ICA is expected to continue. Optionally, the diameter,density, shape and/or packing arrangement of pores 39 may be selectivelyaltered in the region of the vessel branching to ensure that adequateblood continues into the side branch.

Bare stents implanted at a vessel bifurcation may disrupt flow andcreate areas of stagnation susceptible to thrombus formation. Moreover,bare stents may provide inadequate embolic protection in someapplications. The small diameter of pores 39, as compared to thediameter of apertures 36 of stent 32, provides a grating that isexpected to reduce turbulence and allow thrombus-free blood flow intothe side branch.

Referring now to FIG. 13, an alternative embodiment of the presentinvention is shown in use at a vessel bifurcation. Apparatus 70 issimilar to apparatus 30 of FIGS. 8-12, except that apparatus 70comprises radial opening 76 that is expected to allow unimpeded bloodflow to a vessel side branch at the point of stenting. Apparatus 70comprises balloon-expandable or self-expanding stent 72 having lumen 73.Preferably, at least a portion of stent 72 is radiopaque. Biocompatiblematerial 74 having pores 75 is attached to stent 72. Radial opening 76extends through stent 72 and material 74, thereby providing a side pathfor blood flow out of lumen 73.

Pores 75 of material 74 are sized such that apparatus 70 is impermeableto stenotic emboli larger than a predetermined size, but is permeable torapid ingrowth of endothelial cells. Pores 75 preferably have a minimumwidth of approximately 30 μm and a maximum width of approximately 100μm, and even more preferably have an average width of about 80 μm. Also,apparatus 70 may optionally comprise coating or attached active groupsC, as discussed hereinabove with respect to apparatus 30.

In FIG. 13, apparatus 70 has been expanded to a deployed configurationwithin common carotid artery CCA and external carotid artery ECA. Priorto expansion of apparatus 70, radial opening 76 was aligned withinternal carotid artery ICA to ensure uninterrupted and unimpeded bloodflow through the side branch. In addition to maintenance of flow,apparatus 70 provides enhanced embolic protection, facilitates rapidendothelialization, and reduces the risk of restenosis and thrombusformation.

Prior to expansion of apparatus 70, radiopacity of stent 72, or otherradiopaque features associated with apparatus 70, may facilitate thealignment of opening 76 with the side branch. Alternatively,Intravascular Ultrasound (“IVUS”) techniques may facilitate imaging andalignment. In this case, the delivery catheter for apparatus 70 also maycomprise IVUS capabilities, or an IVUS catheter may be advanced into thevessel prior to expansion of apparatus 70 (not shown). MagneticResonance Imaging (“MRI”) or Optical Coherence Tomography (“OCT”), aswell as other imaging modalities that will be apparent to those of skillin the art, alternatively may be used.

Additional embodiments of the present invention may be provided with aplurality of radial openings configured for use in vessels exhibiting aplurality of branchings. The present invention is expected to beparticularly indicated for use in the carotid and femoral arteries,although embodiments also may find utility in a variety of othervessels, including the coronary and aortic arteries, and in non-vascularlumens, for example, in the biliary ducts, the respiratory system, orthe urinary tract.

With reference now to FIGS. 14 and 15, exemplary techniques formanufacturing apparatus 30 of the present invention are provided. Othertechniques within the scope of the present invention will be apparent tothose of skill in the art.

Biocompatible material 38 preferably comprises a modified thermoplasticpolyurethane, and even more preferably a siloxane modified thermoplasticpolyurethane. The material preferably has a hardness in the range ofabout 70 A to 60 D, and even more preferably of about 55 D. Othermaterials and hardnesses will be apparent to those of skill in the art.Material 38 preferably is formed by a spinning process (not shown), forexample, as described in U.S. Pat. No. 4,475,972 to Wong, which isincorporated herein by reference. Material 38 is heated to form aviscous liquid solution that is placed in a syringe. The material isadvanced by a piston or plunger through a fine nozzle, where thematerial flows out onto a rotating mandrel as fine fibers. The finefibers form a fibrous mat or covering of biocompatible covering material38 on the rotating mandrel. As material 38 cools, the fibers solidify,and adjacent, contacting fibers are sintered to one another. Controllingthe number of layers of fiber that are applied to the rotating mandrelprovides control over the porosity of material 38.

If material 38 is to be sintered to stent 32, this may be achieved bydisposing the stent over the mandrel prior to laying down material 38(not shown). Material 38 also may be attached to either the internal orexternal surface of stent 32. FIGS. 14 and 15 provide various attachmentschemes for attaching material 38 to a surface of the stent.

In FIG. 14A, stent 32 is attached with adhesive 80 to material 38 alongall or most of structure 34 of stent 32. Adhesive 80 may comprise, forexample, a material similar to biocompatible material 38, but with adifferent melting point. For example, adhesive 80 may comprise amodified thermoplastic polyurethane with a hardness of about 80 A. Stent32 is dipped in the adhesive and dried. Then, stent 32 and material 38are coaxially disposed about one another, and the composite apparatus isheated to a temperature above the melting point of adhesive 80, butbelow the melting point of biocompatible material 38. The compositeapparatus is then cooled, which fuses material 38 to stent 32, therebyforming apparatus 30.

A drawback of the attachment scheme of FIG. 14A is that the quantity ofadhesive used in forming apparatus 30 may add a significant amount ofmaterial to the apparatus, which may increase its delivery profileand/or its rigidity. Additionally, a risk may exist of adhesiveparticles coming loose during collapse or expansion of apparatus 30. Ifreleased within a patient's vasculature, these particles may act asemboli.

FIG. 14B provides an alternative attachment scheme. Material 38 isattached with adhesive 80 to stent 32 at discrete points 82, or isattached along defined planes, such as circumferential bands,longitudinal seams, or helical seams (see FIG. 15). Such attachmentreduces the amount of adhesive material required, which, in turn, mayreduce rigidity, delivery profile, and a risk of embolization ofadhesive particles.

Referring to FIGS. 15A-15D, various techniques for attaching a stentcovering to a stent, in a manner that provides the attachment scheme ofFIG. 14B, are provided. In FIGS. 15A-15C, biocompatible material 38 isconfigured for disposal along an interior surface of stent 32.Obviously, the material may alternatively be prepared for disposal aboutan exterior surface of the stent.

In FIG. 15A, biocompatible material 38 has been formed on mandrel M.Material 38 then is coated with longitudinal seams 84 of adhesive 80,and stent 32 is loaded over the material. Adhesive 80 bonds stent 32 tomaterial 38 along seams 84. In FIG. 15B, material 38 is provided withhelical seams 86 of adhesive 80, while in FIG. 15C, material 38 isprovided with circumferential bands 88 of adhesive 80. In FIG. 15D,stent 32 is provided with adhesive 80 at discrete points 82. Points 82may be on either the internal or external surface of stent 32, andbiocompatible material 38 then is loaded onto to either the internal orexternal surface respectively. Additional adhesive configurations willbe apparent to those of skill in the art.

While preferred illustrative embodiments of the present invention aredescribed hereinabove, it will be apparent to those of skill in the artthat various changes and modifications may be made therein withoutdeparting from the invention. The appended claims are intended to coverall such changes and modifications that fall within the true spirit andscope of the invention.

1. A method of reducing thrombus formation in a vessel of a vasculaturecomprising: providing an apparatus having a tubular expandable memberand a membrane, the tubular expandable member having inner and outersurfaces and proximal and distal ends, the membrane being disposed aboutthe tubular member, the membrane including a plurality of pores;coupling the tubular member to a delivery system; advancing the tubularmember in a collapsed delivery configuration within the vessel; anddeploying the apparatus from a collapsed configuration to an expandedconfiguration in which the apparatus engages a wall of the vasculatureat a treatment site, the membrane providing a smooth surface for fluidflow.
 2. The method according to claim 1, wherein the tubular member isconstructed of a metal mesh.
 3. The method according to claim 2, whereinthe membrane is disposed about the outer surface of the tubular member.4. The method according to claim 3, wherein the membrane extends beyondthe proximal and distal ends of the tubular member.
 5. The methodaccording to claim 1, wherein the membrane is disposed about the innersurface of the tubular member.
 6. The method according to claim 1,wherein the membrane is produced by a weaving, knitting, or braidingprocess.
 7. The method according to claim 1, wherein the pores have aminimum width of approximately 30 μm or more.
 8. The method according toclaim 7, wherein the pores have a maximum width of approximately 100 μmor less.
 9. The method according to claim 1, wherein the membrane isconfigured to promote endothelization of the tubular member.
 10. Themethod according to claim 1, wherein at least one of the pores is sizedto allow blood flow therethrough.
 11. The method according to claim 10,further including a radial opening formed in the web pattern, wherein atleast one of the pores configured to allow blood flow therethrough ispositioned within the radial opening.
 12. The method according to claim1, wherein the tubular member is self-expanding.
 13. The methodaccording to claim 1, wherein the tubular member is balloon expandable.14. The method according to claim 1, wherein the pores formed in themembrane are uneven in size and placement.
 15. The method according toclaim 1, wherein the tubular member is a stent.
 16. The method accordingto claim 16, further including the step of recrossing a lumen of thestent with a balloon catheter and of expanding the balloon within thelumen of the stent.